Constraining the optical potential in the search for η-mesic 4He

A consistent description of the dd→4Heη and dd→ (4Heη)→boundX cross sections was recently proposed with a broad range of real (V0) and imaginary (W0), η−4He optical potential parameters leading to a good agreement with the dd→4Heη data. Here we compare the predictions of the model below the η production threshold, with the WASA-at-COSY excitation functions for the dd→3HeNπ reactions to put stronger constraints on (V0,W0). The allowed parameter space (with |V0|<∼ 60 MeV and |W0|<∼7 MeV estimated at 90% CL) excludes most optical model predictions of η−4He nuclei except for some loosely bound narrow states.